Morbidity and mortality associated with Chagas disease in Latin America exceed better-known conditions such as malaria, tuberculosis, or AIDS. Millions of people are affected by this trypanosomiasis. No vaccines are available to prevent this disease and drug treatments have serious side effects and are not completely effective. The study of metabolic pathways in these parasites that may be essential for their survival but may not find an equivalent counterpart in their host could make possible the development of specific inhibitors as possible means of controlling the parasites without damaging the hosts. One of the most interesting characteristics of Trypanosoma cruzi, the etiologic agent of Chagas disease, is its possession of two closely associated organelles, the acidocalcisomes and the contractile vacuole. Acidocalcisomes are acidic calcium stores rich in pyrophosphate (PPi) and polyphosphate (polyP). The contractile vacuole is present in free-living protists and also in Leishmania spp., but has not been described in T. brucei, while acidocalcisomes are present in all trypanosomatids. Our preliminary results suggest that the contractile vacuole is a trafficking hub for the transfer of proteins important for the pathogenesi of T. cruzi infection to the plasma membrane. We have found that trans-sialidases, which are important for the establishment of T. cruzi infection, are trafficked through the contractile vacuole in their way to the plasma membrane. PolyP is a linear polymer of a few to many hundreds of phosphate (Pi) residues linked by high-energy phosphoanhydride bonds and is ubiquitous from bacteria to mammals. In contrast to several functions ascribed to polyP in bacteria, the functions of this polymer in eukaryotic cells are relatively undefined. With the discovery of the potent modulatory activity of this polymer on blood coagulation and inflammation there has been renewed interest in this molecule as of potential importance in virulence of polyP-containing microorganisms. Recent results from our laboratory suggest that polyP and/or PPi could be involved in the pathogenesis of T. cruzi infection. We propose to study the roles of acidocalcisomes and the contractile vacuole in the pathogenesis of T. cruzi infection.